AC Milan's hopes of qualifying for next season's Champions League suffered a setback after they were beaten 2-0 by Torino on Sunday, their first Serie A defeat to the Turin club since November 2001.
The win lifted Torino to 56 points, level with Milan, but the Turin club moved ahead of Gennaro Gattuso's side and Atalanta into fifth place due to their superior head-to-head record over both sides.
"Things aren't going our way, we are struggling, but I saw the performance we needed," Gattuso told Sky Sport Italia.
"Torino force you to play badly, we created chances, but when you give away a penalty in such a naive manner, you're going to lose your temper.
"For a while we were used to knowing how to suffer for a result, but now something keeps happening and the team struggles to react."
Roma occupy the fourth and final Champions League spot on 58 points, but Atalanta (56) have the chance to overtake them by beating Udinese on Monday.
Gattuso is facing increasing pressure to keep his job after his side picked up just one win in their past eight games in all competitions.
In contrast, Torino are now unbeaten in six games, confirming their status as the surprise package in this season's race for a top-four finish in Serie A.
"We are having less fun than two months ago and that takes a toll. We're not sharp, we think too much and that saps your enthusiasm," Gattuso added.
"This is why I say that I can't get in the heads of the players, as I want them to have the eye of the tiger, a constant grit and determination, but it's not happening.
"I am tied to results, I am responsible. We are not only having embarrassing results for our team, we're embarrassing an historic club."
Mazzarri was sent to the stands for protests early in the second half but his side took the lead soon after when Franck Kessie pushed Armando Izzo in the back to concede a penalty, which Belotti converted calmly.
Milan came close to an equaliser as Tiemoue Bakayoko's header struck the crossbar, but Torino soon doubled their lead when Berenguer gathered a poor headed clearance from Mateo Musacchio before firing a volley into the roof of the net.
Things went from bad to worse for the visitors when Romagnoli was shown a red card for sarcastically applauding a refereeing decision.
With four rounds remaining, just three points separate Roma in fourth place from Lazio in eighth.